I would be a LEGO collector/builder. Spend my etire life on eBay, Bricklink, LEGO.com buying all the sets I could. Then merge them into one unstoppable space drednought. Maybe a Mass Effect Reaper. I would use the bricks of those I defeat to make my Reaper even more unstoppable.

(Don't try to beat me by saying you would have the Normandy. That only happened because Shepard defeted Saren in the Citadel, thus weakening Sovereign's shields.)